Owing to their high-electron mobilities and direct band gaps, III-V compound semiconductors are ideal for many electronic and optoelectronic applications such as high-performance transistors, photovoltaics, LEDs, and photodetectors. The development of epitaxial growth techniques such as molecular beam epitaxy, metal-organic chemical vapor deposition (MOCVD), and pulsed laser deposition have enabled the growth of single-crystalline III-V thin films with excellent performance for device applications. In order to obtain such high-quality single-crystalline thin films, the growth needs to be performed on a closely lattice-matched substrate.